Method of making selenium elements



June 19, 1945. IQ s s w ETAL 2,378,438

' METHOD OF MAKING SELENIUM ELEMENTS Filed May 1, 1943 IN VEN TORS orro 545 V Patented June 19 1945 METHOD or MAKING SELENIUM ELEMENTS Otto Saslaw, Lyndlmrst, and Harry Carlson, Newark, N. J., asslgnors to Federal Telephone & Radio Corporation, New York, N. Y., a corporation of Delaware ApplicationMay 1, 1943, Serial No. 485,280-

rciaims. (c1. its-306) s This invention relates to selenium elements and particularly to'a method of making them and has for itsobiect to improve and facilitate the making of such elements.

As is well known, selenium elements such as rectifiers and photocells commonly consist of an adherent layer of crystalline selenium on 'a carrier plate and s. counter-electrode over the selenium.

Such elements have been made by spreadin molten selenium over the base plate, allowing it to cool and harden and then crystallizing the hardened selenium by means of a heat treatment, after which the counter-electrode has been applied, commonly by spraying a molten alloy such as Woods metal over the selenium surface.

According to my invention the selenium is applied to the base plate by blowing it on in powdered form under. considerable pressure while the base plate is maintained at an-elevated temperature. Under these conditions the powder particles, by a sintering action, adhere to the baseplate and closely adhere to each other forming a thin solid layer of selenium. After a suitable thickness of the layer has been blown on in this manner. the element is further heat-treated and provided with a counter-electrode in the usual manner.

The invention will be better understood from the following detailed description in conjunction with the accompanying drawing; of which Fig. 1 illustrates a perspective view of apparatus for spraying the selenium on the base plate;

Fig. 2 illustrates a faceview of a seleniumcoated element; and

Fig. 3 illustrates a sectional view of the element shown in Fig. 2.

Referring to Fig. 1, the base plate I may be in the usual form of a disc such as iron or steel or aluminum or the like and is ordinarily roughened and may be nickel plated if desired. According the arrow. The front end of hose I terminates in a mouth 6, which may be of glass, having a nozzle I which enters the throat of an elongated receptacle 8, which may also be glass, in which it is held by a suitable stopper 9 which may be for example of rubber having a hole through it which (fits over mouth 6. The delivery end ll! of receptacle 8 is narrowed down as shown and preferably filled with a suitable filtering device such as a wad of steel wool H to act" as a filter for powder passing through it. There is fitted over delivery to a"- oommon practice the disc is shown with a central hole 2. The disc is placed on a table 3 which is heated preferably to a temperature at which the powder particles will adhere to the base plate and closely adhere to each other to form a coherentor solid layer of selenium, suitable temperatures under said conditions being within the range of about 100 to element in is shown for'this purpose. The upper surface of the base plate is sprayed from a spray nozzle l3 with a let 4 of selenium powder under substantial pressure, as shown. The spraying apparatus comprises a tubing or i which may be of rubber, into which comair is blown in the direction shown by 150' C. An electric heating end l0 a tubing l2, for example rubber, which terminates in the nozzle [3, which may be of glass.

The selenium powder I4 is placed-in the enlarged receptacle 8 so that when the compressed air or other compressed fluid is blown into receptacle 8, the powder is blown through filter ll. into tube ID from whence it is blown through spray nozzle l3 under high velocity on to'the base plate. The selenium powder may be made in a well-known manner, for example, by melting solenium and then grinding-it up into the powder form. The air pressure used is not especially critical but should be suflicient to produce a good adherence of the selenium on the plate. It the pressure istoo low, it may be foundthat the adherence will be poor and there is furthermore not as good an effect on the electrical properties. An air pressure of 5 to 7 pounds per square inch has been used satisfactorily and the allowable presthe powder velocity will be correlated, with the base plate temperature so that-the combined ef- 3 feet will produce ,the required coalescence. Thishas been referred to herein as sintering; but the invention will be operativewhenever the powder particles adhere to each other and to the base 'plateto form the required solid layer of selenium,

regardless of whether this coalescence may accurately be described technically as sintering.

The selenium powder thus blown on the base plate i apparently softens orsinters somewhat upon striking the heated plate and the powder particles adhere to the plate and to each other forming a uniform layer of the desired thickness. A suitable thickness for the layer is around .004 to .008 inch. The high pressure propulsion of the powder on the heated plate has a beneficial effect on the selenium element because itis found that the selenium can be placed in a satisfactory conductive condition by a..simp1e heat treatment in an oven at a temperature "somewhat below the melting point of selenium, for example around 200 C. to 214C. for about a half hour or thereabout and without the necessity for the application of further pressure on the The selenium may then be given any suitable surface treatment, as desired, following which the counter-electrode may be applied. r.

Figs. 2 and 3 show a selenium element made according to Fig. 1, with the layer I! 01' selenium on the base plate and the counter-electrode alloy l6 over the selenium. To place it in condition it need only be electro-formed by the application of a steady or pulsating D. C. voltage in the direction opposite the direction of normal forward current flow.

By propelling the powder on the heated plate in accordance with this invention there is provided a single method of producing a crystalline selenium layer on a carrier plate, which requires only a relatively short and simple heat treatment thereafter. The usual heat treatment over a much longer period of time, involving the application of pressure against the selenium by means of a pressure plate, is avoided.

What isclaimed is:

1. The method of making a selenium element which comprises blowing selenium powder under pressure on a heated base plate.

2. The method of making a selenium element which comprises blowing selenium powder under air pressure on a base plate heated to a temperature at which the powder particles adhere to each other'and to the carrier plate.

3. The method of making a selenium element which comprises blowing selenium powder by pressure on a base plate heated to a temperature at which the powder particles adhere to each other and to the base plate and then further heattreating the selenium-coated element at a temperature somewhat below the melting point of selenium.

4. The method or making a selenium element which comprises blowing selenium powder on a base plate at a pressure of around five to seven pounds per square inch, said base plate being heated to about to C. and then further heat-treating the selenium-coated element at a temperature somewhat below the melting point of selenium.

5. The method of making a selenium element which comprises blowing selenium powder by pressure on a base plate heated to about 100 to 150 C., then further heat-treating the seleniumcoated element at an elevated temperature somewhat'below the melting point of selenium and then placing a counter-electrode layer over the selenium surface.

6. The method of making a selenium element which comprises blowing selenium powder by pressure on a base plate heated to about 100 to 150 0., then further heat-treating the seleniumcoated element at an elevated temperature somewhat below the melting point of selenium, then applying a counter-electrode layer over the seleniuni surface and then electro-forming the element by applying to it a D. C. voltage in the direction opposite that of normal forward current flow.

'7. The method of making a selenium element which comprises forming a sintered layer of selenium on a base plate by propelling selenium powder against the base plate heated to sintering temperature at a velocity suflicient to produce good adhesion, and thereafter consolidating the selenium by heat treatment at an elevated temperature somewhat below the melting point of selenium.

' OTTO SASLAW.

HARRY CARLSON. 

